Field
This application relates to medical devices configured to generate bubbles. Such devices may be particularly useful for cardiovascular procedures, such as to detect the presence of Patent Foramen Ovale (“PFO”), Atrial Septal Defects (“ASD”), shunts in the heart, or other septal defects.
Description of the Related Art
The normal human heart, depicted in FIG. 1, can act as two biological pumps, side by side, sharing a common wall called a septum, and sharing one electrical network. The right side heart has two chambers known as the right atrium and the right ventricle. The left side heart also has two chambers known as the left atrium and the left ventricle. The right side of the heart receives deoxygenated blood from the body in its right atrium. The blood then goes into the right ventricle, which pumps the blood toward the lungs for oxygenation. From the lungs, oxygenated blood goes to the left atrium. From the left atrium the blood goes into the left ventricle, which then pumps the oxygenated blood through the body. In a normal heart, the left ventricle is the most powerful chamber capable of pushing the oxygenated blood into the body to meet body's metabolic demand.
The fetal heart, depicted in FIG. 2, is different from the adult heart. In a fetus, the lungs are still growing and not yet ready to receive blood for oxygenation. Two connections in the fetal heart help blood to bypass lungs of the fetus. One such connection is the Patent Foramen Ovale (“PFO”), which is a hole located in the septum that separates the left and right atria. This hole allows the blood to go from the right atrium to the left atrium bypassing the lungs. Another connection is the Patent Ductus Arteriosus (“PDA”), which is located between the pulmonary artery and the aorta. A majority of the blood is redirected through the PFO to bypass the lungs. However, a small amount of blood still enters the right ventricle, but is then redirected into the aorta through the PDA. With the help of both these connections, the PFO and the PDA, blood is prevented from going into immature fetal lungs.
Soon after birth the PFO and the PDA should close naturally, and blood should be directed toward the lungs of the newborn for oxygenation. From the lungs, the oxygenated blood goes to the left atrium and then to the left ventricle, from where it is pumped to fulfill the body's oxygen and other nutritional requirements.
Unfortunately, in 27% to 35% of people the PFO fails to close after birth (See, Attaran, Robert R., Imran Ata, Vijayasree Kudithipudi, Laura Foster, and Vincent L. Sorrell. “Protocol for Optimal Detection and Exclusion of a Patent Foramen Ovale Using Transthoracic Echocardiography with Agitated Saline Microbubbles.” Echocardiography 23.7 (2006): 616-22. Web). This condition may be associated with numerous medical problems, including, but not limited to stroke, paradoxical embolism, cryptogenic stroke, and migraines. If blood clots developed in the veins detach, they normally travel to the right side of the heart, from which they may continue up to the lungs. When a PFO, ASD, or other shunts or septal defects are present, depending on pressure conditions between right and left atriums, small clots may flow from the right atrium to the left atrium, thus allowing a clot to bypass the lungs. Any clot that bypasses the lungs and reaches the left heart poses a great risk of interfering with the blood supply to tissues and organs to which it flows. For example, when such a clot enters an artery in the brain it may cause a stroke. Thus, correct and timely detection of a PFO/ASD is critical in preventing potentially serious medical problems.